Liquid heater, in particular an electric kettle, usually requires a thermosensitive temperature control apparatus to control power-off protection of the liquid heater in the case of abnormal heating. The thermosensitive temperature control apparatus is usually mounted to an electric heater, so as to realize better thermal contact. According to market feedback on quality problems, when the product is first used, the performance is not influenced distinctly even when the product is still heated after water is dried. However, as the number of use increases, the heater would turn yellowish black due to slow temperature sensing, causing electric heating components to burn out. This is because the electric heater and the thermosensitive temperature control apparatus work under alternate cold and hot states, and inner stress and deformation of components mounted therein can be caused by the thermal shock. In this case, contact between the thermosensitive temperature control apparatus and the electric heater becomes under tightened due to the deformation. As a result, thermosensitivity of an overheating protection component is gradually reduced, rendering the product to fail and burn out. In design state, the thermosensitive temperature control apparatus is rigidly connected to the electric heater, and limit is realized through screw locking and a top surface of a support frame of the thermosensitive temperature control apparatus, so that a contact surface between the thermosensitive temperature control apparatus and the electric heater can become immobile after assembly. In the meantime, in order to eliminate bad contact caused by manufacture error, a product called “thermal conductive silicone grease” is usually coated on the thermalsensitive components in the thermosensitive temperature control apparatus in the existing technology, so that better thermal conduction can be realized. However, a temperature control apparatus and a heating tube of the electric kettle work in a misty environment, which is defined in safety standards as the third degree polluted environment, causing the “thermal conductive silicone grease” to age or dry. As a result, the sensing effect of the thermosensitive temperature control apparatus is influenced.
Therefore, in order to avoid product safety problem due to this reason, the national safety standards GB4706.19 prescribes requirement for 100 times of thermal shock tests. However, the deformation is closely related to the production technology, and is difficult to control during manufacturing of the product or be noticed during use of the product by a consumer. The above defects are hidden and hard to prevent.